Method and system for focusing and registration in electron beam projection microfabrication

ABSTRACT

A method and system for improved focusing and registration in an electron beam device including an electron beam source, condenser lenses, deflection coils, projection lenses, a mask and a target. The deflection coils are located between second and final condenser lenses and deflect the focused electron beam onto a projection mark on the mask and onto a similar registration mark on the target to provide superimposed images for registration purposes.

United States Patent Broers et al.

METHOD AND SYSTEM FOR FOCUSING AND REGISTRATION IN ELECTRON BEAMPROJECTION MICROFABRICATION Inventors: Alec Nigel Broers, PurdysStation;

Marcus Barry Heritage, Katonah, both of NY.

Assignee: International Business Machines Corporation, Armonk, NY.

Filed: Dec. 28, 1973 Appl. No.: 429,438

Related US. Application Data Continuation-impart of Ser. No. 267,844.June 30, 1972. abandoned.

Foreign Application Priority Data Primary Examiner-James W. LawrenceAssistant livaminer-B. C. Anderson Attorney, Agent, or Firm-Graham S.Jones, ll; John J. Goodwin [57] ABSTRACT A method and system forimproved focusing and registration in an electron beam device includingan electron beam source, condenser lenses, deflection coils,

r- 28, 1 3 United Kingdom 14834/73 projection lenses, a mask and atarget. The deflection June 4, 1973 Japan 48-62080 il are l catedbetween econd and final condenser June 6, 1973 France ..73.2l785 lensesand deflect the focused electron beam onto a June 23, 1973 Germany2332091 projection mark on the mask and onto a i il i 0.5. CI. 250/492;250/398; 250/491 F P 9; :9 target pmvde super'mpmd rm. Cl. H0lj 37/00'mages PurPOses- Field of Search 250/492, 491, 398, 31 l,

250/396 18 Claims, 18 Drawing Figures Y GENERATOR BLANKING 3 ARPL I; 226 IIAIIuAL 21L 1 x GENERATOR ADJ. csT

cuRRERr M30 x AMPLITUDE AND vARIARLE orrsEr O\ CONTROLS,56 F 65 l l 62 lx CURRENT AMPLIFIER l J 5 T l Y AMPLITUDE AND I vARIAIILE OFFSET norms,as L Q Q 59 54 efi Y CURRENT AMPLIFIER i- Y VIDEO ADJ. r

mSPLAY PWR SPLY o o ADJ. 0ST 51 cuRRERr Wm PIIIR SPLY mm PHOTOMULTIPLIERPMHMUAPR 8i975 3,876,883

sum 3 0f 4 FIG. 70

FIG. 7A

FIG.7B FIG. 70

FIG. 8C

FIG. 8D

SHEET 0f 4 FIG 8A FIG. 88

FIG. 9C

FIG.9D

FIG. 9A

FIG.9B

METHOD AND SYSTEM FOR FOCUSING AND REGISTRATION IN ELECTRON BEAMPROJECTION MICROFABRICATION CROSS REFERENCE TO RELATED APPLICATION Thisapplication is a continuation'in-part of copending patent applicationSer. No. 267,844, filed on June 30, 1972 now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to electron optical projection systems formicrofabrication and methods of focusing and registration therefor, anduse thereof.

2. Prior Art Electron beams such as used in electron beam tubes havebeen focused by lenses and deflected by magnetic fields in the priorart. A typical example of such a sys tem is described in US. Pat. No.2,991,361 issued July 4, 1961 to Karl-Heinz Herrmann.

Another example of focusing an electron beam is set forth in US. Pat.3,3 19,1 10, Electron Focus Projection & Scanning System, issued May 9,1967 to Kurt Schlesinger.

A distinction of the present invention over the prior art is theprovision of a registration hole in a mask and a registration mark on atarget which is used in combination with a deflection coil for providingradiation focused to form an image of the hole upon the registrationmark on the target and employing such registration in an electron beamprojection system to prepare for exposure of the entire target.

US Pat. No. 3,118,050 issued to J. S. Hetherington Jan. 14, 1964 showsan electron beam system with a microfabrication target and without abeam deflection system. The source of electrons passes through a singlevariable focus condenser or collimating type of magnetic lens. The lensfloods the beam at once over all of the area of a projection mask havingfiducial notches in the edge thereof through which rays of the electronbeam may pass. The condenser type lens has an adjustable D.C. supplyconnected to opposite ends of the coil, which apparently can be adjustedto collimate the electrons passing through the lens. A focusing systemincluding a pair of magnetic lenses is located between the mask and thework piece holder. The focusing lenses are also connected to adjustableD.C. supplies. The holder includes spaces for workpieces, and around theperiphery of such spaces are fiducial notches each containing a terminalinsulated from the holder. A balanced pair comparator circuit isemployed to help to register the holder, while the holder is moved byadjusting of micrometer screws, until the balanced pair indicates properpositioning. The only means for viewing the position of the work holderand work is through a binocular microscope. The balanced pair and thebinocular microscope are totally independent means for measuring theposition of the holder via the balanced pair and the work as well, viathe optical microscope.

No prior art has been found however, which deals with the problem oflocating thespecific orientation of the work in the holder relative to amask to be used. In addition an optical microscope type of sensor doesnot provide sufficient magnification for the small kinds ofmicrocircuits being developed in electronics today. Also, any radiationprojected by Hetherington floods the entire surface of the workpiececausing radiation exposure of the entire surface of the workpiece whenthe workpiece has not yet been registered. This is unacceptable in caseswhere the radiation must be shielded from the workpiece until after ithas been registered in the proper position. Furthermore, Hetheringtondoes not indicate how the radiation is to be applied during registrationother than to say the beam is directed at the work and that the beamvaries up to a maximum voltage, a maximum pulse rate and a maximumcurrent, and that intensity can be varied. No suggestion is made as tohow the beam can be prevented from performing work upon the workpieceduring holder registration. Thus, Hetherington registers only the holderand thus fails to register the work itself, and apparently exposes theworkpiece to harmful radiation, prior to alignment.

In addition none of the prior art suggests scanning a pencil beamfocused upon a mask with windows through the mask onto a workpiece.

SUMMARY OF THE INVENTION An object of the present invention is animprovement to an electrorioptical projection system wherein aprojection pattern is focused and accurately registered on an unexposedwafer.

Another object of the present invention is to provide an electron beamprojection system including a set of deflection coils located proximateto condenser lenses to focus and deflect the electron beam ontoregistration marks.

The foregoing and other objects, features, and advantages of the presentinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows in a schematic manner theimaging portion of an electron beam column for optical projection andcontrol circuits therefore in accordance with the principles of thepresent invention.

FIG. 2 is an illustration of superimposed registration images for thecases where the marks and thereby their images are similaranddissimilar.

FIG. 3 is a plan view of a mask for an electron beam projectionmicrofabrication system.

FIG. 4 is a video display of a semiconductor wafer target registrationmark with a shadow of a registration grid projected by the electron beamfrom a mask, with both images out of focus.

FIG. 5 is a view similar to FIG. 4 with the shadow grid in focus.

FIG. 6 is a view similar to FIG. 5 with the wafer also in focus.

FIG. 7 (A-D) is a set of video displays of projections of fourregistration windows in a mask upon a single wafer where excessive scalecauses a mismatch of registration.

FIG. 8 (A-D) is a set of video displays of the marks in FIG. 7 (A-D)after the scale has been readjusted, by reducing magnification in theprojection system.

FIG. 9 (A-D) is a set of video displays of the marks in FIG. 8 (A-D)after registration has been realigned.

DESCRIPTION OF A PREFERRED EMBODIMENT In electron projection optics, asin light optics, the function of the condenser lens system is toilluminate the projection mask and then collect all the electron beamspassing through the mask and focus them into the entrance pupil of theprojection lens system.

Because of the extreme tolerances required in the fabrication ofmicrocircuits by electron beam projection optics, it is very importantthat the electron image of the mask be focused and that the projectionmask and the target wafer be registered with respect to each other. Inthe past, electron beam tube projection systems have been used in thefabrication of microcircuits on semiconductor wafers in a manner similarto the way light optics in microcircuit cameras are used tophotographically reproduce circuit patterns contained on light masksonto semiconductor wafers.

Some examples of the use of electron beam projection technology in thefabrication of microcircuits are described in the publication ElectronOptical Microminiaturization of Stencils by H, Koops, G. Mollenstedt andR. Speidel, Optik 28 (5) pgs. 518-531 (1968/69) and an Electron ImagingSystem For the Fabrication of Integrated Circuits by T. W. OKeeffe, .I.Vine and R. M. Handy, Solid State Electronics, Pergamon Press 1969, Vol.12, pp. 841-848. These publications discuss the use of electron beamoptics in microminiaturization and are hereby incorporated by reference.Accordingly, the fundamentals of electron beam tube operation includingelectron beam sources, magnetic lenses, focusing, deflection systems andthe like are presumed to be known to those of described skill in the artand will not be explained or describe in unnecessary detail in thepresent disclosure.

An embodiment of the present invention is shown schematically in FIG. 1.The structure of FIG. 1 is capable of illuminating a suitable projectionmask with electrons and imaging the mask onto a semiconductor targetwafer to fabricate a microcircuit in a manner described in the priorart. In FIG. 1, however, an additional mode of operation is shown andwill be described wherein the electron beam optics can be operated in ascanning and in a preliminary focusing and registration mode, as well.

Referring to FIG. 1, an electron beam tube microcircuit fabricationstructure 24 is shown in the focusing and registration mode, alsoreferred to as the probe mode. The structure 24 evacuated to about Torrincludes a conventional electron beam gun 28 of about KV which producesbeams of electrons, for example, from a tungsten cathode. The electronbeam is directed through blanking electrodes 25, 26 aperture 27 a firstmagnetic condenser lens 30 powered by adjustable constant current powersupply 70 and a second magnetic condenser lens 32 powered by adjustableconstant current power supply 71 which lenses focus the electron beam.In the present invention, prior to the final condenser lens 38 poweredby adjustable constant current power supply 72, a set of orthogonal Xdeflection coils 34 and Y deflection coils 36 are positioned in a planewhich is an image of aperture 44 through lenses 38 and 42. Duringregistration rather than have the electron beam impinge the entireprojection mask 40, the condenser lens system is readjusted to provide apinpoint focus upon mask 40. The deflection coils 34 and 36 areenergized by waveforms adapted to cause the electron beam to be directedthrough the final condenser lens 38 in such a direction that theelectron beam is focused at a specific location on projection mask 40 atwhich there is located a unique registration pattern in the form of ahole 41 of a selected configuration.

In light beam projection systems for microcircuit fabrication, theprojection mask is usually a transparent substrate on which the desiredcircuit is graphically layed out using light opaque material. Inelectron beam projection systems, the projection mask such as 40 in FIG.1 and FIG. '3 with circuit apertures 39 and registration mark apertures41 can be analogous to light optics. Here the mask is preferably aphotolithographically manufactured very thin (0.2 mil thick)selfsupporting, electro-formed grid, or pattern of copper gold or nickelwhich forms the electron opaque sections where desired. The grid isformed on a substrate and then lifted off it to produce theself-supporting foil. The electron beam is to pass through the openingsin the mask and impinge on the target wafer thereby exposing the uppersurface of the target wafer, which may be silicon or silicon oxidecoated with an electron sensitive resist, with the desired circuitpattern. Yet again, it may be a cathode mask such as described in theaforementioned reference of OKeeffe et al. where now the mask itself isthe source of electrons for the projec tion mode of operation. The mask40 is rotatably mounted to be turned by worm gear 78.

In circuit fabrication, it is important that the projection mask beproperly registered and aligned with the target wafer. In the embodimentof the present invention illustrated in Flg. 1, the deflection coils (orplates) 34 and 36 are provided to deflect the electron beam over themask 40 and wafer 48 when a deflection current (or voltage) is appliedto the coils. The value of the deflection current is a function of thetype of deflection coils employed, the geometry of the projection systemand the design of the magnetic lenses. This will vary from system tosystem and the deflection current in a given system can be determined byone having ordinary skill in electron beam technology. In the generalcase, including projection systems without a physical aperture, one ortwo sets of orthogonal coils may be positioned above, within or afterthe lens 38 previous to the mask such that the direction of theprincipal ray of the spot focused at the mask plane is such that the raypasses through the center of the effective entrance pupil of theprojection optics.

In FIG. 1, the lens 38 previous to the mask focuses the electron beam atthe plane of the mask. The focused spot, which is smaller than anydimension of the registration mark is scanned by the coils 34 and 36over a registration hole configuration 41 in the mask 40. This may beany of the three types of mask described except that when the cathodemask is used, the accelerating electrostatic potential of the electrongun 28 is thesame as the electrostatic potential of the cathode mask.The focused beam that passes through the registration hole 41 thenpasses on through the projection optics, which consists of theprojection lens 42 powered by constant current power supply 73, aperture44 shifting deflection coils 79 and 80 associated with aperture 44powered by variable supplies 74, for shifting the focus pointtransversely a small amount and final projection lens 46 powered byvariable supply 76, and onto the target wafer 48 where anotherregistration mark is located. The projection mask 40 and target wafer 48are in alignment when the images of the registration marks on the wafersurface are superimposed with the shadow images 41 in FIG. 2 of theregistration mark mask openings 41.

The aforesaid is accomplished in the following manner. A signal, whichmay take the form of backscattered electrons detected by the electrondetector 50, is amplified and displayed by a video display 52 scanned insynchronism with the deflection coils 34 and 36. The scanning systemincludes X generator 55 and Y generator 54, which respectively drive Xand Y amplitude and variable offset control units 56 and 58 having X andY control knobs 62 and 64 respectively for amplitude which are shownmechanically ganged by line 93 for display magnification control and Xand Y offset control knobs 63 and 65 respectively. Outputs are providedfrom X and Y units 56 and 58 to X and Y current amplifiers 57 and 59connected to coils 34 and 36 respectively. Separate outputs from controlunits 56 and 58 are connected to the scanning input circuits of videodisplay 52. Electron detector 50 comprises an electron scintillatorreceiving electrons 66 and a light pipe connecting the scintillator to aphoto multiplier 51 which drives video amplifier 53 to control theintensity of video display 52. Knobs 62, 63, 64 and 65 make it possiblefor the beam to be adjusted to scan certain portions of the large mask40 shown in cross section by reducing the amplitude, or the entire mask40 and all apertures therein with larger amplitude control settings. Thezero offset can be used to adjust the beam location for work in anygiven small area when a small amplitude signal is applied. In general,the signal may be detected by any of the methods known to those skilledin the art of scanning electron microscopy. Assuming that the surface oftarget wafer 48 is coincident with the projection image plane, videodisplay 52 will produce two superimposed images one of the surface oftarget wafer 48 with the registration mark and any other surface featureperfectly focused. The second image will be a shadow image of mask 40due to the chopping of the electron beams in the mask plane by the maskitself. It is to be noted that because the projection optics shown inFIG. I remain the same in both the pro jection mode and the focusingmode as shown, the correspondence between the two superimposed videoimages is the same as between the mask and its projected image exceptthat dimensions appearing the same in both video images are in factrelated by the projection magnification.

Alignment of mask 40 to target wafer 48 is achieved with reference toFIG. 2 by using registration patterns 41 or 41A in mask 40 and shapedmarks 43 on target wafer 48 which may. but need not be similar in shapeto the holes in the mask. FIG. 2 shows examples of a similar holepattern 41 and mark 43 and a dissimilar hole pattern 141' and mark 143,both examples being shown superimposed to indicate mask and waferalignment. Registration of mask and wafer is complete when the videooutput shows the images of both marks superimposed as shown in FIG. 2for all registration points on the object. The ultimate limit on theaccuracy of registration is determined by the size of the electron beamprobe in the image plane, which itself is only limited by the edgeresolution in the projection optics. Any displacement in the mask fromits appropriate conjugate plane results in a defocusing of the maskshadow image. Similarly, displacement of the wafer results in adefocusing of the wafer image. Thus, the wafer 48 and the mask 40 can befocused one to the other as appropriate and also the two can beaccurately registered.

Focusing and Registration Procedure To achieve correct focusing of thebeam upon the mask and the wafer (workpiece) as well as correctregistration, three separate conditions must be satisfied. l The maskand wafer planes must be conjugate with respect to projection lenses 42and 46 (i.e. the mask and wafer are in focus on the video displaybecause the scanning beam is in focus as it reaches each of thoseplanes.) (2) The demagnification of the projection system must bemaintained to a very high degree of accuracy. (3) The mask and wafermust be aligned in both X and Y translations and rotation.

Satisfaction of the above conditions is obtained by the proceduresoutlined below. FIGS. 4-9 (D) show video displays with a mesh gridalignment mask and a cross marked on the substrate in various stages ofadjustment. The image of the mesh grid is superposed upon the image ofthe cross on the wafer plane.

First Condition Step: Focusing To satisfy the first condition above, theobjective is to correct the defocussing.

Step (la) is to adjust the current to condenser coil 38 until the maskgrid image in FIG. 4 is in focus as in FIG. 5.

Step (lb) is to adjust current in projection coil 46 to focus the largerimage of the wafer marking 96 as in FIG. 6.

Demagnification Adjustment Now the mask and wafer planes are both infocus. However, the projection demagnification if inaccurate must beadjusted. If it is inaccurate, then the result will be similar to thatshown in FIG. 7, (A-D) where the mask size projected onto the wafer istoo small. While mask projection 41A is aligned with its wafer mark,wafer marks 96B and 96D are both too high relative to the maskprojections and wafer marks 96C and 96D are too far to the right oftheir corresponding mask projections. Thus, it is obvious that the maskdemagnification must be changed to achieve similar relative positioningof all marks. Thus, the next step is to adjust current to thedemagnification coils 42 and 46 from power supply units 73 and 76, sothat the grid image remains focussed but the display shows similarrelative positioning of all marks. Since the mark projections41A',41B,41C and 41D are widely spaced on the projection onto the waferthe scale can be adjusted to an extremely high order of accuracy. Ofcourse, the scan of the coils 34 and 36 must look at each one of thoseregistration patterns alone without scanning the intermediate areas. Aproblem has arisen as shown in FIG. 8 (AD) in the course ofdemagnification, since marks 96A and 41A are no longer aligned correctlybecause as the whole pattern shrank, for example, 96A moved up away from96D while 96D moved towards 96A and a correct position.

Alignment The alignment of the mask image and wafer can be adjusted inX, Y and rotation. The rotation is handled mechanically either byturning worm gear 78 attached to the support for mask 40 or by worm 91attached to turn the table 92 supporting wafer 48.

While X, Y alignment is originally adjusted by knobs on micrometerdrives 82, 83 to move intermediate support tables 84, 85, now deflectioncoils 79, 80 can be supplied a slightly different current by powersupplies 74, 75 respectively to align the grids with the crossesproperly as shown in FIG. 9 (AD). Note that the above steps may berequired to be performed in a cyclical sequence of iterations ofcorrection to achieve proper alignment.

Exposure After the alignment step, the work is in position ready forexposure of the work through the mask and now the electron beam canexpose the work piece in the desired kind ofa way by flooding orscanning as de sired through the mask. Note, that the registration marks43 on the wafer are made initially, with an extra thickness layer ifrequired to prevent subsequent operationssuch as etching from removingthem, as for example where photo resist is being developed to providewindows for etching, which windows would expose the marks for etchingalso. See Hatzakis U.S. Pat. No. 3,519,788.

An added feature of the invention is that the probe mode of operation asshown in FIG. 1 can be used to determine if any aberrations exist in theprojection optics. When optimum focusing of both the shadow image of themask opening and the wafer surface has been achieved, the relativedifference in definition of the wafer surface features and the shadowimage across the field of view gives an indication of the defocusingeffect of coma, astigmatism and field curvature in the projectionoptics. Similarly comparing the distortion of the shadow image, if anyexists, with that of the surface features of the wafer, can yield theprojection distortion coefficient.

When the X or Y generator 54, 55 is retracing, a signal on line 97 or 98respectively operates blanking amplifier 90 via line 99 to operateblanking electrodes to deflect the electron beam away from the aperturein aperture 27. Amplifier 90 can be operated manually also for timing ofexposures in projection mode.

Variation in the configuration of the projection optics using magneticlenses is possible and the structure is not necessarily limited to thatshown in the drawings. For example, the final condenser lens and thefirst projection lens can be merged into one single field lens with themask situated in the center of the focusing field. Under thesecircumstances, it is necessary to introduce an additional lens betweenthe second condenser lens and the field lens in order to focus the probeat the mask plane. Except for this difference, all other operations inthe probe mode are similar to those described. In general, the requiredsize of the intermediate source image (after second condenser lens 32)in the projection and the probe modes will be different. Thus, it isexpected that the changes in strength of the first and second condenserlenses will be required when switching form one mode to the other.Again, the changes in lens strengths are within the skill of workers inelectron beam technology.

While the invention has been particularly shown and described withreference to a preferred embodiment, it will be understood by thoseskilled in the art that the foregoing and other changes in form anddetails may be made therein without departing form the spirit and scopeof the invention.

What is claimed is:

l. A method for operating an electron beam wafer exposure systemincluding a target whose position is adjustable, a source of an electronbeam, a projection mask for said target having a registration holetherein, means for focusing said beam on said mask, means for scanningsaid focused beam across said mask, means for projecting radiation fromsaid beam in the image form through said mask onto said target, meansfor sensing beam radiation projected onto said target, means fordisplaying a scanned input connected to receive the output of said meansfor sensing for display, means for providing scanning signals havingoutputs connected to drive said means for scanning and said means fordisplaying in synchronism, wher'eby radiation projected onto said targetthrough said mask is displayed upon said display, said target having aregistration mark thereon, the steps comprising focusing said beamsubstantially only upon said registration hole in said mask, viewingsaid display, adjusting the position of said target until the displayshows that said beam is focused upon said hole, and then broadening thefocus of said beam to cover substantially all of said mask.

2. In a method for focusing and registration of an electron beamprojection system including a source of an electron beam, a projectionmask having a unique pattern of registration electron beam windowstherein, an adjustable focal length condenser lens system locatedbetween said electron source and said projection mask including electronlenses for collecting said electron beam from said source and directingsaid beam onto said projection mask, a target wafer having a uniqueregistration marks on the surface thereof, a projection lens systemlocated between said projection mask and said target wafer forcollecting electron beams passing through said projection mask anddirecting them onto said target wafer, a deflection system locatedbetween said source and said mask for scanning said electron beam acrosssaid mask, said deflection system cooperating with said condenser lenssystem to scan the focus of said electron beam across the plane of saidprojection mask at one of said registration windows and said projectionlens system operating to focus the portion of said electron beam passingthrough a said window in said mask onto the surface of said targetwafer, and electronic detection means for sensing the image projectedthrough said mask onto said wafer, the improvement comprising, focusingsaid electron beam into a pencil point beam upon a point upon saidprojection mask, scanning said pencil point beam to hit a registrationwindow in said mask, viewing said detection means to determine whethersaid electron beam is directed towards said registration mark on thesurface of said target wafer, and adjusting the position until said beamis directed towards said mark, and then changing the focus of saidcondenser lens system to adjust said beam to flood said projection maskand to project through all of the windows therein upon said targetwafer.

3. A method for operating an electron beam wafer exposure systemincluding a target whose position is adjustable, a source of an electronbeam, a projection mask for said target having plural widely spacedregistration holes therein, first means for focusing said beam on saidmask, means for scanning said focused beam across said mask, means forprojecting radiation from said beam in the image form through said maskonto aaid target, means for sensing beam radiation projected onto saidtarget, means for displaying a scanned input connected to receive theoutput of said means for sensing for display, means for providingscanning signals having outputs connected to drive said means forscanning and said means for displaying in synchronism, whereby radiationprojected onto said target through said mask is displayed upon saiddisplay, said target having a registration mark thereon, the stepscomprising focusing said beam substantially only upon said registrationholes in said mask, viewing said display. adjusting the scale relativethe position of said beam of said target until the display shows thatsaid beam is generally focused upon said holes, adjusting the scale ofthe projection of said mask to match the spacing of said registrationmarks upon said target, adjusting the alignment of the projectionthrough said holes upon said registration marks and then broadening thefocus of said beam to cover substantially all of said mask.

4. A method in accordance with claim 3 wherein said first means isadjusted to focus said beam upon said mask by adjusting the control ofsaid first means to yield a focused image of the scanned portion of saidmask upon said display, and adjusting said means for projection to focussaid beam passing through said mask upon said target, prior to adjustingscale and alignment of said projection.

5. A focusing and registration system for an electron beam projectionsystem comprising:

a source of an electron beam,

a projection mask having a unique pattern of registration electron beamwindows therein,

a condenser lens system located between said electron source and saidprojection mask including electron lenses for collecting said electronbeam from said source and focusing said beam onto a point on saidprojection mask,

a target wafer having a unique registration mark on the surface thereof,

a projection lens system located between said projection mask and saidtarget wafer for collecting electron beams passing through saidprojection mask and directing them onto said target wafer,

a deflection system located between said source and said mask forscanning said electron beam across said mask, said deflection systemcooperating with said condenser lens system to scan the focus of saidelectron beam across the plane of said projection mask at one of saidregistration windows and said projection lens system operating to focusthe portion of said electron beam passing through a regis tration windowin said mask onto the surface of said target wafer,

and electronic detection means for sensing the image projected throughsaid mask onto said wafer.

6. A focusing and registration system according to claim 5 wherein saidprojection mask has holes therein in a predetermined pattern, one ofsaid holes being a unique registration hole.

7. A focusing and registration system according to claim 5 furtherincluding a projection aperture located in said projection lens systemand where a first and second pair of deflection elements are located insaid condenser lens system in a plane conjugate to the plane of saidprojection aperture through all projection lenses between 'said apertureand said mask and at least one condenser lens.

8. A focusing and registration system according to claim 5 wherein saiddetection means is an electron detector responsive to electronsscattered from the surface of or collected by said target wafer.

9. A focusing and registration system according to claim 5 wherein saidcondenser lens system includes a first magnetic condenser lens, a secondcondenser lens and a final condenser lens and wherein said deflectionsystem is located between said second condenser lens and said finalcondenser lens.

10. A focusing and registration system according to claim 5 wherein saidprojection lens system includes a first magnetic projection lens and afinal magnetic projection lens, said aperture being located between saidfirst and final projection lenses and said projection mask being locatedbetween said condenser lens system and said first projection lens.

11. A focusing and registration system according to claim 5 wherein saidfirst and. second pair of deflection elements are first and seconddeflection coils arranged orthogonally with respect to each other.

12. A focusing and registration system according to claim 6 wherein saidregistration hole in said projection mask and said registration mark onsaid target wafer have the same geometrical shapes.

13. A focusing and registration system according to claim 6 wherein saidregistration hole in said projection mask and said registration mark onsaid target wafer are dissimilar in geometric shape.

14. A focusing and registration system according to claim 8 wherein saidelectron detection means includes an electron detector responsive toelectrons from the surface of said target wafer and a video displaymeans connected to said electron detector for visually displaying theprojected image of said registration window in said projection mask onsaid target wafer and the image of said registration mark on the surfaceof said target wafer.

15. A focusing system for an electron beam projection system comprising:

a source of an electron beam,

a projection mask having a unique pattern of windows therein,

a condenser lens system located between said electron source and saidprojection mask including an electron lens for collecting said electronbeam from said source and focusing said beam onto a point on saidprojection mask,

a target,

a projection lens system including at least one lens and an aperturelocated between said projection mask and said target for collecting theportion of said electron beam passing through said projection mask anddirecting it onto said target,

a deflection system for scanning said electron beam across said mask,including deflection elements located between said source and saidprojection mask, said deflection system cooperating with said condenserlens system to scan the focus of said electron beam across the plane ofsaid projection mask across at least one of said windows and saidprojection lens system operating to focus said elec tron beam passingthrough said window in said mask onto a point on the surface of saidtarget.

16. A focusing and registration system for an electron beam electricalcircuit manufacturing system comprisa source of an electron beam,

a projection mask having a unique registration pattern of windowstherein.

a condenser lens system located between said electron source and saidprojection mask including electron lenses for collecting said electronbeam from said source and focusing said beam onto a point on saidprojection mask,

a target electrical circuit material,

a projection lens system including at least one lens and an aperturelocated between said projection mask and said target wafer forcollecting said electron beam passing through said projection mask anddirecting said beam onto said target material,

a deflection system for scanning said electron beam across said masklocated in said condenser lens system in a plane conjugate to the planeof said aperture through all projection lenses between said aperture andsaid mask and at least one condenser lens, said deflection systemcooperating with said condenser lens system to focus and scan saidelectron beam in the plane of said projection mask across at least oneof said registration windows and operating with said projection lenssystem to focus the portion of said electron beam passing through saidwindow in said mask onto a point on the surface of said target material.

17. An electron beam wafer exposure system including,

a target,

a source of an electron beam,

a projection mask for said target,

means for focusing said beam on said mask.

means for scanning said focused beam across said mask,

means for projecting radiation from said beam in the image formed bysaid mask onto said target.

means for sensing beam radiation projected onto said target,

means for displaying a scanned input having a radiation input connectedto receive the output of said means for sensing for display and havingposition inputs for receiving scanning signals,

means for providing scanning signals having outputs connected to drivesaid means for scanning and said position inputs of said means fordisplaying in synchronism. 1

whereby radiation projected onto said target through said mask isdisplayed upon said display.

18. In a method for focusing and registration of an electron beamprojection system including a source of an electron beam, a projectionmask having a unique pattern of registration electron beam windowstherein, an adjustable focal length condenser lens system locatedbetween said electron source and said projection mask including electronlenses for collecting said electron beam from said source and directingsaid beam onto said projection mask, a target wafer having a uniqueregistration mark on the surface thereof, a projection lens systemlocated between said projection mask and said target wafer forcollecting electron beams passing through said projection mask anddirecting them onto said target wafer, a deflection system locatedbetween said source and said mask for scanning said electron beam acrosssaid mask, said deflection system cooperating with said condenser lenssystem to scan the focus of said electron beam across the plane of saidprojection mask at one of said registration windows and said projectionlens system operating to focus the portion of said electron beam passingthrough a said window in said mask onto the surface of said targetwafer, and electronic detection means for sensing the image projectedthrough said mask onto said wafer, the improvement comprising, focusingsaid electron beam into a pencil point beam upon a point upon saidprojection mask, scanning said pencil point beam to hit a registrationwindow in said mask, viewing said detection means to determine whethersaid electron beam is directed towards said registration mark on thesurface of said target wafer, and adjusting the deflection of the beamuntil said beam is directed through said window towards said mark,adjusting power to said condenser lens system to focus said mask aspresented upon said display;

adjusting power to said projection lens system to focus the image ofsaid target wafer upon said display; adjusting the scale of theprojection of said mask shown upon said display to match the spacing ofthe images of said registration windows with corresponding registrationmarks upon said target as shown upon said display; adjusting thealignment of the projection through of said windows upon said marks; andthen changing the focus of said condenser lens system to adjust saidbeam to flood said projection mask and to project through all of thewindows therein upon said target wafer.

1. A method for operating an electron beam wafer exposure systemincluding a target whose position is adjustable, a source of an electronbeam, a projection mask for said target having a registration holetherein, means for focusing said beam on said mask, means for scanningsaid focused beam across said mask, means for projecting radiation fromsaid beam in the image form through said mask onto said target, meansfor sensing beam radiation projected onto said target, means fordisplaying a scanned input connected to receive the output of said meansfor sensing for display, means for providing scanning signals havingoutputs connected to drive said means for scanning and said means fordisplaying in synchronism, whereby radiation projected onto said targetthrough said mask is displayed upon said display, said target having aregistration mark thereon, the steps comprising focusing said beamsubstantially only upon said registration hole in said mask, viewingsaid display, adjusting the position of said target until the displayshows that said beam is focused upon said hole, and then broadening thefocus of said beam to cover substantially all of said mask.
 2. In amethod for focusing and registration of an electron beam projectionsystem including a source of an electron beam, a projection mask havinga unique pattern of registration electron beam windows therein, anadjustable focal length condenser lens system located between saidelectron source and said projection mask including electron lenses forcollecting said electron beam from said source and directing said beamonto said projection mask, a target wafer having a unique registrationmarks on the surface thereof, a projection lens system located betweensaid projection mask and said target wafer for collecting electron beamspassing through said projection mask and directing them onto said targetwafer, a deflection system located between said source and said mask forscanning said electron beam across said mask, said deflection systemcooperating with said condenser lens system to scan the focus of saidelectron beam across the plane of said projection mask at one of saidregistration windows and said projection lens system operating to focusthe portion of said electron beam passing through a said window in saidmask onto the surface of said target wafer, and electronic detectionmeans for sensing the image projected through said mask onto said wafer,the improvement comprising, focusing said electron beam into a pencilpoint beam upon a point upon said projection mask, scanning said pencilpoint beam to hit a registration window in said mask, viewing saiddetection means to determine whether said electron beam is directedtowards said registration mark on the surface of said target wafer, andadjusting the position until said beam is directed towards said mark,and then changing the focus of said condenser lens system to adjust saidbeam to flood said projection mask and to project through all of thewindows therein upon said target wafer.
 3. A method for operating anelectron beam wafer exposure system including a target whose position isadjustable, a source of an electron beam, a projection mask for saidtarget having plural widely spaced registration holes therein, firstmeans for focusing said beam on said mask, means for scanning saidfocused beam across said mask, means for projecting radiation from saidbeam in the image form through said mask onto said target, means forsensing beam radiation projected onto said target, means for displayinga scanned input connected to receive the output of said means forsensing for display, means for providing scanning signals having outputsconnected to drive said means for scanning and said means for displayingin synchronism, whereby radiation projected onto said target throughsaid mask is displayed upon said display, said target having aregistration mark thereon, the steps comprising focusing said beamsubstantially only upon said registration holes in said mask, viewingsaid display, adjusting the scale relative the position of said beam ofsaid target until the display shows that said beam is generally focusedupon said holes, adjusting the scale of the projection of said mask tomatch the spacing of said registration marks upon said target, adjustingthe alignment of the projection through said holes upon saidregistration marks and then broadening the focus of said beam to coversubstantially all of said mask.
 4. A method in accordance with claim 3wherein said first means is adjusted to focus said beam upon said maskby adjusting the control of said first means to yield a focused image ofthe scanned portion of said mask upon said display, and adjusting saidmeans for projection to focus said beam passing through said mask uponsaid target, prior to adjusting scale and alignment of said projection.5. A focusing and registration system for an electron beam projectionsystem comprising: a source of an electron beam, a projection maskhaving a unique pattern of registration electron beam windows therein, acondenser lens system located between said electron source and saidprojection mask including electron lenses for collecting said electronbeam from said source and focusing said beam onto a point on saidprojection mask, a target wafer having a unique registration mark on thesurface thereof, a projection lens system located between saidprojection mask and said target wafer for collecting electron beamspassing through said projection mask and directing them onto said targetwafer, a deflection system located between said source and said mask forscanning said electron beam across said mask, said deflection systemcooperating with said condenser lens system to scan the focus of saidelectron beam across the plane of said projection mask at one of saidregistration windows and said projection lens system operating to focusthe portion of said electron beam passing through a registration windowin said mask onto the surface of said target wafer, and electronicdetection means for sensing the image projected through said mask ontosaid wafer.
 6. A focusing and registration system according to claim 5wherein said projection mask has holes therein in a predeterminedpattern, one of said holes being a unique registration hole.
 7. Afocusing and registration system according to claim 5 further includinga projection aperture located in said projection lens system and where afirst and second pair of deflection elements are located in saidcondenser lens system in a plane conjugate to the plane of saidprojection aperture through all projection lenses between said apertureand said mask and at least one condenser lens.
 8. A focusing andregistration system according to claim 5 wherein said detection means isan electron detector responsive to electrons scattered from the surfaceof or collected by said target wafer.
 9. A focusing and registrationsystem according to claim 5 wherein said condenser lens system includesa first magnetic condenser lens, a second condenser lens and a finalcondenser lens and wherein said deflection system is located betweensaid second condenser lens and said final condenser lens.
 10. A focusingand registration system according to claim 5 wherein said projectionlens system includes a first magnetic projection lens and a finalmagnetic projection lens, said aperture being located between said firstand final projection lenses and said projection mask being locatedbetween said condenser lens system and said first projection lens.
 11. Afocusing and registration system according to claim 5 wherein said firstand second pair of deflection elements are first and second deflectioncoils arranged orthogonally with respect to each other.
 12. A focusingand registration system according to claim 6 wherein said registrationhole in said projection mask and said registration mark on said targetwafer have the same geometrical shapes.
 13. A focusing and registrationsystem according to claim 6 wherein said registration hole in saidprojection mask and said registration mark on said target wafer aredissimilar in geometric shape.
 14. A focusing and registration systemaccording to claim 8 wherein said electron detection means includes anelectron detector responsive to electrons from the surface of saidtarget wafer and a video display means connected to said electrondetector for visually displaying the projected image of saidregistration window in said projection mask on said target wafer and theimage of said registration mark on the surface of said target wafer. 15.A focusing system for an electron beam projection system comprising: asource of an electron beam, a projection mask having a unique pattern ofwindows therein, a condenser lens system located between said electronsource and said projection mask including an electron lens forcollecting said electron beam from said source and focusing said beamonto a point on said projection mask, a target, a projection lens systemincluding at least one lens and an aperture located between saidprojection mask and said target for collecting the portion of saidelectron beam passing through said projection mask and directing it ontosaid target, a deflection system for scanning said electron beam acrosssaid mask, including deflection elements located between said source andsaid projection mask, said deflection system cooperating with saidcondenser lens system to scan the focus of said electron beam across theplane of said projection mask across at least one of said windows andsaid projection lens system operating to focus said electron beampassing through said window in said mask onto a point on the surface ofsaid target.
 16. A focusing and registration system for an electron beamelectrical circuit manufacturing system comprising: a source of anelectron beam, a projection mask having a unique registration pattern ofwindows therein, a condenser lens system located between said electronsource and said projection mask including electron lenses for collectingsaid electron beam from said source and focusing said beam onto a pointon said projection mask, a target electrical circuit material, aprojection lens system including at least one lens and an aperturelocated between said projection mask and said target wafer forcollecting said electron beam passing through said projection mask anddirecting said beam onto said target material, a deflection system forscanning said electron beam across said mask located in said condenserlens system in a plane conjugate to the plane of said aperture throughall projection lenses between said aperture and said mask and at leastone condenser lens, said deflection system cooperating with saidcondenser lens system to focus and scan said electron beam in the planeof said projection mask across at least one of said registration windowsand operating with said projection lens system to focus the portion ofsaid electron beam passing through said window in said mask onto a pointon the surface of said target material.
 17. An electron beam waferexposure system including, a target, a source of an electron beam, aprojection mask for said target, means for focusing said beam on saidmask, means for scanning said focused beam across said mask, means forprojecting radiation from said beam in the image formed by said maskonto said target, means for sensing beam radiation projected onto saidtarget, means for displaying a scanned input having a radiation inputconnected to receive the output of said means for sensing for displayand having position inputs for receiving scanning signals, means forproviding scanning signals having outputs connected to drive said meansfor scanning and said position inputs of said means for displaying insynchronism, whereby radiation projected onto said target through saidmask is displayed upon said display.
 18. In a method for focusing andregistration of an electron beam projection system including a source ofan electron beam, a projection mask having a unique pattern ofregistration electron beam windows therein, an adjustable focal lengthcondenser lens system located between said electron source and saidprojection mask including electron lenses for collecting said electronbeam from said source and directing said beam onto said projection mask,a target wafer having a unique registration mark on the surface thereof,a projection lens system located between said projection mask and saidtarget wafer for collecting electron beams passing through saidprojection mask and directing them onto said target wafer, a deflectionsystem located between said source and said mask for scanning saidelectron beam across said mask, said deflection system cooperating withsaid condenser lens system to scan the focus of said electron beamacross the plane of said projection mask at one of said registrationwindows and said projection lens system operating to focus the portionof said electron beam passing through a said window in said mask ontothe surface of said target wafer, and electronic detection means forsensing the image projected through said mask onto said wafer, theimprovement comprising, focusing said electron beam into a pencil pointbeam upon a point upon said projection mask, scanning said pencil pointbeam to hit a registration window in said mask, viewing said detectionmeans to determine whether said electron beam is directed towards saidregistration mark on the surface of said target wafer, and adjusting thedeflection of the beam until said beam is directed through said windowtowards said mark, adjusting power to said condenser lens system tofocus said mask as presented upon said display; adjusting power to saidprojection lens system to focus the image of said target wafer upon saiddisplay; adjusting the scale of the projection of said mask shown uponsaid display to match the spacing of the images of said registrationwindows with corresponding registration marks upon said target as shownupon said display; adjusting the alignment of the projection through ofsaid windows upon said marks; and then changing the focus of saidcondenser lens system to adjust said beam to flood said projection maskand to project through all of the windows therein upon said targetwafer.